Ok here are some day dreams. Russian rail lines destroyed by death of 10,000 cuts. What I mean is destroy each rail section with very cheap methods. Ok making up this part. Assume you have a cheap way to freeze a small section of track, say two feet. Next thermal shock ( use dragon metal fire) ok did that weaken the rail section to failure? Did it cost less than $10.00.
Launch 10,000 drones, each destroying 100 spots on the rail lines . Use drones to stop repair efforts.
It is just a thought experiment. I wonder if there is a cheap way to destroy 100 miles of track.